The present application relates generally to falling film and hybrid falling film evaporator systems in refrigeration, air conditioning and chilled water systems or process systems.
Certain process systems, as well as refrigeration, air conditioning and chilled water systems, include an evaporator to effect a transfer of thermal energy between refrigerant of the system and another fluid to be cooled. One type of evaporator includes a shell with a plurality of tubes forming a tube bundle through which the fluid to be cooled is circulated. The refrigerant is brought into contact with the outer or exterior surfaces of the tube bundle inside the shell, resulting in a thermal energy transfer between the fluid to be cooled and the refrigerant. In a conventional evaporator, the refrigerant is heated and converted to a vapor state, which is then returned to a compressor where the vapor is compressed, to begin another refrigerant cycle. The cooled fluid is circulated to a plurality of heat exchangers located throughout the building. Warmer air is passed over the heat exchangers where the cooled fluid is being warmed, while cooling the air for the building returned to the evaporator to repeat the process.
For example, some types of evaporators with refrigerant boiling outside the tubes include flooded evaporators, falling film evaporators and hybrid falling film evaporators. In conventional flooded evaporators, the shell is partially filled with a pool of boiling liquid refrigerant in which the tube bundle is immersed.
In a conventional falling film evaporator, a dispenser deposits, such as by spraying, an amount of liquid refrigerant onto the surfaces of the tubes of the tube bundle from a position above the tube bundle, forming a layer (or film) of liquid refrigerant on the tube surface. The refrigerant in a liquid or two-phase liquid and vapor state contacts the upper tube surfaces of the tube bundle, and by force of gravity, falls vertically onto the tube surfaces of lower disposed tubes.
A conventional hybrid falling film evaporator incorporates the attributes of a falling film evaporator and a flooded evaporator by immersing a lesser proportion of the tubes of the tube bundle than the flooded evaporator while still spraying fluid on the upper tubes, similar to a falling film evaporator.
One challenge to the efficient operation of the falling film and hybrid falling film evaporators is that a portion of the fluid vaporizes and significantly expands in volume. The vaporized fluid expands in all directions, causing cross flow, or travel by the vaporized fluid in a direction that is transverse, or at least partially transverse to the vertical flow direction of the liquid fluid under the effect of gravity. Cross flow results in insufficient wetting of tubes of the tube bundle, significantly reducing heat transfer with the fluid to be cooled flowing inside those tubes in the tube bundle.
Another challenge is the compressor, which receives its supply of vaporized fluid from an outlet typically formed in the upper portion of the evaporator, can be damaged if the vaporized fluid contains entrained liquid droplets. Components must be implemented to provide separation between the vapor and liquid droplets. However, these components add to the complexity and cost of the system, and may also result in an undesired pressure drop prior to the vapor refrigerant reaching the compressor.
What are needed are falling film and hybrid falling film evaporators that substantially prevent cross flow caused by expanding vaporizing fluid and which also require less space than a flooded evaporator for liquid droplet separation than a conventional flooded or existing designs of flooded film or hybrid evaporators.
Intended advantages of the disclosed systems and/or methods satisfy one or more of these needs or provides other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.